The present invention relates to a waste carbonization method which carbonizes and/or activates solid wastes using other wastes.
Here, solid wastes include {circle around (1)} wastes such as municipal wastes or material formed by compressing and molding the wastes, {circle around (2)} wood wastes among demolition and construction wastes, {circle around (3)} wood wastes produced from forest thinning, and {circle around (4)} wastes produced from food processing, such as strained draff of beer. However, any wastes may be used as long as the wastes contain carbon. It is also possible to replace the solid wastes with materials such as wood chips which are not wastes. Other wastes may be either the above-described solid wastes or lower-quality or lower-carbon-content solid or liquid wastes. Other wastes may be replaced with fuel such as coal which is ordinarily used.
When organic matter is heated under appropriate conditions, the organic matter is converted through pyrolysis to a carbon-rich material, i.e., amorphous carbon. This reaction is called carbonization. According to conventional carbonization, about 10 to 20% (wet basis) of a carbonous material is converted to charcoal (in the case of wood), although this value depends on a manufacturing process. The reason why the carbonization yield is low is that a part of carbon contained in the carbonous material is slowly burned as a heat source for the carbonization. Although 80 to 90% of the carbonous material is converted into steam and gas which are then discharged, the amount of carbon dioxide discharged is also large because a part of the carbon contained in the carbonous material is burned as a heat source for the carbonization.
Further, there is a technology for producing activated carbon in a single stage from vegetable-type or mineral-type materials. According to this method, while the vegetable-type or mineral-type materials are in contact with gas containing 0.5 to 5% of oxygen by volume, calcination is carried out at a temperature of 400xc2x0 C. or higher in the case of vegetable materials, and at a temperature of 500xc2x0 C. or higher in the case of mineral materials to produce activated carbon. However, this method involves an economical problem, because the concentration of oxygen in gas is adjusted by adding nitrogen, argon or helium to combustion exhaust gas of coal or petroleum and valuable material is used for raw material. Specifically, the concentration of oxygen in the combustion exhaust gas is so high that expensive inert gas is necessary to adjust the oxygen concentration to 1 to 2% optimum for activation.
On the other hand, according to statistics in 1991, the annual production of wood wastes in Japan is about 36 million m3, and more than 90% thereof is not re-utilized and is treated by incineration and reclamation. The wood wastes are mainly derived from demolition of houses or construction of houses, and about 74% of all of the wood wastes is occupied by such wood wastes. The wood wastes derived from demolition of houses have been subjected to preservative treatment such as CCA (chromium-copper-arsenic) treatment. Incineration or reclamation of those wood wastes leads to a fear of causing the following environmental problems: As (arsenic) is mixed into incineration exhaust gas; a high concentration of Cr (chromium) or Cu (copper) is contained in incineration ash; and arsenic, chromium or copper is eluted from landfill site.
At the present time, as a method for treatment or disposal of such wood wastes which have been subjected to preservative treatment, the following are considered: {circle around (1)} a method in which incineration is carried out in a furnace completely equipped with an exhaust gas purification system, and incineration ash and fly ash are stabilized and then discarded in a landfill site; {circle around (2)} a method in which the wood is crushed and then discarded in landfill site; and {circle around (3)} a method in which heavy metals are removed by extraction with a solvent.
These methods, however, have the following problems. In the method {circle around (1)}, a dedicated incineration furnace equipped with an exhaust gas purification system for recovering heavy metals, and a stabilization system for stabilizing incineration ash and fly ash are necessary to thus increase treatment cost. In the method {circle around (2)}, the elution of arsenic, chromium, or copper produced by decayed degradation of the wood into leachate must be prevented, and a problem of the utilization of the land after reclamation remains unsolved. In the method {circle around (3)}, there are many unknown technical matters, and it is difficult to completely remove heavy metals from the wood.
Accordingly, the objects of the present invention are as follows:
(1) to suppress the utilization of carbon, contained in a carbonous material, as a heat source for carbonization to increase the carbonization yield, thereby reducing the amount of CO2 generated (i.e., to minimize the combustion of carbon contained in the carbonous material) during carbonization;
(2) to adjust the concentration of oxygen in the surrounding gas without use of valuable materials such as nitrogen, argon, or helium; and
(3) to produce activated carbon from wood wastes containing harmful materials, and make generated gas completely harmless.
Object (3) will be now described. An attempt has been made to utilize the porosity of charcoal produced from woods, and to utilize charcoal, for example, as adsorbents, moisture control materials, deodorants, and water purification agents. Further, in the iron and steel industry, the effective utilization of scrap should be promoted. Scrap contains organic matter such as plastics, paints, or oils, and there is a fear of producing harmful substances such as dioxin in a dissolution process. In case of a refuse incineration furnace, although the utilization of materials having a large adsorption capacity, such as activated carbon, is effective for the removal of harmful materials produced in the refuse incineration furnace, the use of activated carbon incurs increasing cost. Accordingly, the production of inexpensive and highly adsorptive charcoal from wood wastes to utilize the resultant charcoal as an adsorbent in a steel manufacturing process and a refuse incineration process may promote effective utilization of.wood wastes and reduce the total environmental load. One of the methods for the realization of this system is to produce charcoal having an excellent adsorption ability. Up to now, studies on technology for producing charcoal industrially and studies on conditions for producing charcoal having an excellent adsorption ability are insufficient. Accordingly, one of the subjects of the present invention is the above-mentioned object (3).
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for producing charcoal and/or activated carbon from solid wastes, in which the solid wastes are exposed indirectly or directly to gas generated in pyrolysis gasification or combustion of other wastes and/or fuel.
Here, the term xe2x80x9ccarbonizationxe2x80x9d means that solid wastes as carbonous organic matter are heated and dry-distilled to produce a carbon-rich solid. The activation refers to the formation of micropores (fine pores) around macropores created by volatilization of volatile materials in the course of carbonization by heating in the presence of steam. In general, activated carbon is produced through two processes of carbonization and activation. On the other hand, according to the present invention, the carbonization and the activation are simultaneously carried out in one process, that is, through a series of steps in a single furnace.
According to the present invention, the following are possible: {circle around (1)} to suppress the consumption of carbon, contained in a carbonous material, as a heat source for carbonization to increase the carbonization yield, thereby suppressing the amount of CO2 generated; {circle around (2)} to adjust the concentration of oxygen in the gas without the use of valuable materials such as nitrogen, argon, or helium; and {circle around (3)} to produce charcoal or activated carbon from solid wastes such as wood wastes containing harmful materials, and make generated gas completely harmless.
According to another aspect of the present invention, there is provided a method for carbonizing and/or activating solid wastes, in which a casing containing the solid wastes is exposed to, gas generated in pyrolysis gasification of other wastes.
According to the present invention, the solid wastes contained within the casing are dry-distilled by indirect heating and are consequently converted to gas and charcoal. A part of the generated gas is cooled and condensed to obtain pyroligneous acid, while the remaining gas is returned to a gasification furnace, or a slagging combustion furnace in a subsequent stage.
According to a further aspect of the present invention, there is provided a method for producing charcoal and/or activated carbon from solid wastes, in which the solid wastes are exposed directly to gas generated in pyrolysis gasification of other wastes and/or fuel, or are dry-distilled by the generated gas.